As shown in FIGS. 9 and 10, as an example of an electronic component to be mounted on a mounting board, there is shown a light-emitting diode. The light-emitting diode 2 has a light-emitting element 4, a substrate 6 on which the light-emitting element 4 is mounted, and a pair of patterned electrodes 8 and 10, which are formed to extend from the upper surface to the side surfaces of the substrate 6, or a pair of through hole electrodes 12. Note that the light-emitting element 4 is electrically connected to the pair of patterned electrodes 8 and 10 or the pair of through hole electrodes 12 and then sealed in a resin. The light-emitting are of the light-emitting diode 2 includes the light-emitting element 4 and a resin portion for sealing the light-emitting element 4. A mounting board 16 has a pass-through hole 14, so that the light-emitting area of the light-emitting diode 2 is inserted into the pass-through hole 14 of the mounting board 16. The light-emitting diode 2 is mounted by inserting the light-emitting area of the light-emitting diode 2 into the pass-through hole 14; allowing part of the upper surface of the substrate 6, on which the light-emitting element 4 has been mounted, to be brought into contact with the lower surface of the mounting board 16 such as a circuit board; and then soldering the pair of patterned electrodes 8 and 10 or the pair of through hole electrodes 12 to a pair of patterned electrodes 18 provided on the lower surface of the mounting board 16 to form a solder fillet 20, respectively (for example, see Patent Literature 1).
In this manner, the light-emitting diode 2 can be mounted by allowing part of the upper surface of the substrate 6 of the light-emitting diode 2 to be brought into contact with the lower surface of the mounting board 16, so that the light-emitting area of the light-emitting diode 2 composed of the light-emitting element 4 and the resin portion in which the light-emitting element 4 is sealed is received within the pass-through hole 14 of the mounting board 16. This makes it possible to reduce the overall thickness when compared with the case of mounting the light-emitting diode 2 not in the pass-through hole but on a surface of the mounting board 16. However, the solder fillet 20 for soldering the light-emitting diode 2 is located on the lower surface of the mounting board 16 and cannot be seen from above the upper surface of the mounting board 16. Thus, the solder fillet 20 cannot be visually checked, so that the mounting board 16 had to be turned upside down in order to check the condition of the solder. On the other hand, as shown in FIG. 11, the solder 21 that is located between the lower surface of the mounting board 16 and the upper surface of the substrate 6 of the light-emitting diode could not be visually checked from outside, thereby raising the problem of a check being required to be made by means of X-ray or the like.
It was thus necessary to provide at least the pair of patterned electrodes 8 and 10 which extend around the side surfaces of the substrate 6 of the light-emitting diode or the pair of through hole electrodes 12 which penetrate through the substrate 6. However, a light-emitting diode with a substrate having a metal base such as of aluminum and a wiring plate superimposed one on the other would be more expensive than one with an insulating substrate because it is difficult to provide the patterned electrodes extending around the side surfaces and the through hole electrodes. Accordingly, as shown in FIG. 12, it has been suggested that a wiring plate 24 should be set to be greater than a base 22 so as to allow a pair of electrode portions 26 provided respectively on a pair of opposite ends of the wiring plate 24 to overhang and to be thereby soldered to the lower surface of a mounting board 28 (for example, see Patent Literature 2).
However, when the base 22 was provided with a heat sink 30, the soldered portion of the light-emitting diode shown in FIG. 12 could be visually checked with difficulty even when turned upside down. Furthermore, the overhang portion of the wiring plate 24 had a low strength and thus tended to be damaged when subjected to, for example, the weight of the base 22 or the heat sink 30.